Carotenoid cleavage oxygenase (CCO) is an enzyme that can catalyze carotenoids to volatile aromatic substances and participate in the biosynthesis of two important phytohormones, i.e., abscisic acid (ABA) and strigolactone (SL). However, the genome-wide identification and analysis of the CCO gene family in the rare and endangered woody plant Liriodendron chinense has not been reported. Here, we performed a genome-wide analysis of the CCO gene family in the L. chinense genome and examined its expression pattern during different developmental processes and in response to various abiotic stresses. A total of 10 LcCCO genes were identified and divided into 6 subfamilies according to the phylogenetic analysis. Subcellular localization prediction showed that most of the LcCCO proteins were located in the cytoplasm. Gene replication analysis showed that segmental and tandem duplication contributed to the expansion of this gene family in the L. chinense genome. Cis-element prediction showed that cis-elements related to plant hormones, stress and light response were widely distributed in the promoter regions of LcCCO genes. Gene expression profile analysis showed that LcNCED3b was extensively involved in somatic embryogenesis, especially the somatic embryo maturation, as well as in response to heat and cold stress in leaves. Furthermore, qRT-PCR analysis showed that LcNCED3b obviously responded to drought stress in roots and leaves. This study provides a comprehensive overview of the LcCCO gene family and a potential gene target for the optimization of the somatic embryogenesis system and resistance breeding in the valuable forest tree L. chinense.

Superoxide dismutase (oxide dismutase) is an enzyme synthesized via the expression of SOD-related genes. It is the first line of defense against oxygen free radicals, and it widely exists in the cytoplasm, chloroplasts, and mitochondria. However, the SOD gene family of woody plant Liriodendron chinense has not been studied. To reveal the potential role of SOD genes, we systematically identified and analyzed the SOD gene family of L. chinense, and investigated the transcriptional responses of LcSOD genes to several abiotic stresses, including cold, heat, and drought. A total of eight SOD genes were identified, namely, five Cu/Zn-SODs, two Fe-SODs, and one Mn-SOD, and they were divided into two subgroups according to phylogenetic analysis, gene structure, and conserved motifs. Cis-acting element analysis reveals various hormones and stress respond as cis-acting elements in the promoters of LcSODs. Gene expression analysis shows that most LcSOD genes were in response to abiotic stresses at the transcriptional level. These results help in clarifying the function of LcSOD genes under abiotic stresses, and provide potential targets for the improvement in abiotic stress tolerance in the endangered L. chinense.

Cunninghamia lanceolata (Lamb.) Hook. (Chinese fir) is an important timber species that is widely cultivated in southern China. However, the shallow root system and weak drought resistance of Chinese fir are not enough to cope with high temperature and drought. In recent years, molecular biology has been used to modify plants to make them more resilient. Therefore, improving heat and drought resistance of Chinese fir by molecular biology technology is one of the best choices, whereas fewer genetic information resources for C. lanceolata limit more comprehensive molecular studies. In this study, single-molecule full-length transcriptome (SMRT) sequencing technology was used to obtain full-length transcriptome data on Chinese fir. A total of 21,331 transcripts were obtained via co-assembly, and 11,094 gene sets were obtained via further de-redundancy. In addition, gene function annotation and gene structure analysis were performed. We also used these data to identify nine heat shock transcription factors (Hsfs) in Chinese fir, and heat stress transcriptome and real-time quantitative polymerase chain reaction (PCR) analyses revealed expression changes in response to heat stress, indicating that these may play roles in heat resistance. These studies have enriched the genetic information resources of Chinese fir, which may be utilized for further species promotion, improvement, and application.